Question

A thin disc of radius $b\, = \,2a$ has a concentric hole of radius '$a$' in it (see figure). It carries uniform surface charge '$\sigma$' on it. If the electric field on its axis at height '$h$' $(h < < a)$ from its centre is given as '$Ch$' then value of '$C$' is :

• A. $\frac{\sigma}{a\epsilon_{0}}$
• B. $\frac{\sigma}{2a\epsilon_{0}}$
• C. $\frac{\sigma}{4a\epsilon_{0}}$
• D. $\frac{\sigma}{8a\epsilon_{0}}$

Answer 1

Answer: (C)

$\frac{\sigma}{4a\epsilon_{0}}$

Answer 2